Method of forming epi film in substrate trench

ABSTRACT

The present disclosure provides a method of fabricating a semiconductor device that includes providing a semiconductor substrate, forming a trench in the substrate, where a bottom surface of the trench has a first crystal plane orientation and a side surface of the trench has a second crystal plane orientation, and epitaxially (epi) growing a semiconductor material in the trench. The epi process utilizes an etch component. A first growth rate on the first crystal plane orientation is different from a second growth rate on the second crystal plane orientation.

PRIORITY DATA

This application claims priority to Provisional Application Ser. No.61/256,431 filed on Oct. 30, 2009, the entire disclosure of which isincorporated herein by reference.

BACKGROUND

When a semiconductor device such as a metal-oxide-semiconductorfield-effect transistors (MOSFETs) is scaled down through varioustechnology nodes, high-k dielectric material and metal gate are adoptedto form a gate stack. Strained structures utilizing epitaxy silicongermanium (SiGe) and silicon carbon (SiC) films may be used to enhancecarrier mobility. In addition, channel-last integration schemes may alsobecome a requirement for low melting temperature III-V high mobilitychannel materials such as InAs and InSb to avoid impact from highthermal budget associated with source/drain formation. However, currenttechniques to form these strained structures and channel-lasttransistors have not been satisfactory in all respects. For example, SiN-channel strain is limited to problematic SiC films and no solution forGe P-channel strain has been found. It is even more challenging torealize epitaxy films for channel-last transistors with conventionalepitaxial growth techniques.

SUMMARY

One of the broader forms of an embodiment of the present inventioninvolves a method of fabricating a semiconductor device. The methodincludes providing a semiconductor substrate; forming a trench in thesubstrate, wherein a bottom surface of the trench has a first crystalplane orientation and a side surface of the trench has a second crystalplane orientation; and epitaxially (epi) growing a semiconductormaterial in the trench. The epi process utilizes an etch component. Afirst growth rate on the first crystal plane orientation is differentfrom a second growth rate on the second crystal plane orientation.

Another one of the broader forms of an embodiment of the presentinvention involves a semiconductor device. The semiconductor deviceincludes a semiconductor substrate and a transistor. The transistorincludes a gate structure disposed over the substrate and strainedsource and drain features having a strained film structure.

Yet another one of the broader forms of an embodiment of the presentinvention involves a method of fabricating a semiconductor device. Themethod includes providing a semiconductor substrate; forming a trench inthe substrate, wherein a first surface of the trench has a first crystalplane orientation and a second surface of the trench has a secondcrystal plane orientation; and performing an epitaxial (epi) growthprocess to grow an epi film in the trench, the epi growth processincorporating an etch component. A first growth rate on the firstcrystal plane orientation is different from a second growth rate on thesecond crystal plane orientation such that the etch component prohibitsgrowth on one of the first and second crystal plane orientations.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flow chart of a method of forming an epi film in a substratetrench utilizing a bottom-up growth technique according to variousaspect of the present disclosure;

FIGS. 2A-2C are cross-sectional views of an epi film being formed in asubstrate trench according to the method of FIG. 1;

FIG. 3 is a flow chart of a method of fabricating a semiconductor devicewith strained structures according to various aspects of the presentdisclosure;

FIGS. 4A-4F are cross-sectional views of an embodiment of asemiconductor device at various stages of fabrication according to themethod of FIG. 3; and

FIGS. 5A-5D are perspective views of another embodiment of asemiconductor device at various stages of fabrication.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a first feature over or on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

Referring to FIG. 1, illustrated is a flow chart of a method 50 offorming an epi film in a substrate trench using a bottom-up growthtechnique according to an embodiment of the present disclosure. Themethod 50 begins with block 52 in which a semiconductor substrate isprovided. The method 50 continues with block 54 in which a trench isformed in the substrate. The trench includes a bottom surface with afirst crystal plane orientation and side surface with a second crystalplane orientation. The method 50 continues with block 56 in which an epifilm is formed in the trench by a bottom-up growth technique. Thebottom-up growth technique comprises an epitaxial growth process thatincorporates an etch component. A growth rate on the first crystal planeorientation is different from a growth rate on the second crystal planeorientation.

Referring to FIGS. 2A-2C, illustrated is a crystal structure beingformed according to an embodiment of the method 50 of FIG. 1. In anembodiment, a crystal is grown in a substrate such as a silicon (Si)trench. The crystal may be the same or different from the substrate. Invarious embodiments, the crystal includes Si, SiGe, Ge, SiC, or othersuitable semiconductor materials. In FIG. 2A, a semiconductor substrate102 is provided which includes a silicon (Si) substrate or othersemiconductor substrate, such as Ge or III-V compound semiconductor, ina crystalline structure. In another embodiment, the semiconductorsubstrate 102 may include an epitaxial (epi) layer. A trench 104 isformed in the substrate 102 by an etching or other suitable process. Thetrench 104 includes a bottom surface 106 that has a crystal planeorientation, e.g., [100], and side surfaces 108 that have a crystalplane orientation, e.g., [110] or [111]. It should be noted thatspecified crystal plane orientations are mere examples and that othercrystal plane orientations may be utilized as will be apparent in lightof the discussion that follows.

In FIG. 2B, a bottom-up growth process 110 is performed to grow anepitaxial film (epi film) in the substrate trench 104. Accordingly, thebottom-up growth process utilizes a precursor or precursors. In the caseof Ge epi growth, GeH4 may be used having a flow rate ranging from about5 to 10 sccm with an etch component 120 such as HCl having a flow rateranging from about 10 to about 30 sccm. In some embodiments, the etchcomponent 120 may includes other Cl, or Br containing gases such as Cl2,BCl3, BiCl3, and BiBr3. In other embodiments, F containing gases such asNF3 and HF may be used, however, some of the STI oxide and otherdielectric (SiO2, SiN) hard-mask may be etched by such F based gases.The bottom up growth process 110 implements a temperature suitable forthe epi film growth. For Ge epi growth, a temperature ranging from about450 to about 550° C. and a total pressure ranging from about 20 to 760Torr could be used. It should be noted that the etch component such asHCl is sensitive to the temperature and thus the temperature can betuned to achieved the desired etching effect as discussed below.Further, it is understood that other ranges may be used in applicationswith different types of crystal materials.

The growth rate on the bottom surface 106 is different from the growthrate on the side surfaces 108 due to the different crystal planeorientations of the substrate 102 such as silicon. In an embodiment, ithas been observed that Ge growth on the [100] crystal plane (bottomsurface 106) is about three times (3×) faster than the Ge growth on the[110] crystal plane (side surfaces 108). Further, the Ge growth rate onsilicon [111] crystal plane is expected to be slower than on silicon[110] crystal plane. Accordingly, the bottom-up growth process 110incorporates the etch component 120 to promote bottom-up Ge growth bypreventing Ge from growing on the side surfaces 108 of the silicontrench 104. For example, Ge is grown from the bottom surface 106 of thesilicon trench 104 at a higher rate than that of Ge grown from the sidesurfaces 108 of the silicon trench 104. The etch component 120 removesthe Ge disposed on the side surfaces 108 as well as some Ge disposedfrom the bottom surface 106. However, since the Ge growth rate from thebottom surface 106 is greater than from the side surface 106, the neteffect is that Ge will substantially grow from the bottom-up.

In FIG. 2C, the bottom-up growth process 110 continues until a desiredthickness is achieved. It is noted that there will be some dislocationdefects at the bottom portion if lattice mismatch is substantially largebetween substrate and epi film. As such, there will be a portion of theepi film crystal at the bottom portion 130 of the trench that includesdislocation defects due to mismatch between the substrate lattice andthe epi film lattice. Ge epi growth in a Si trench is a typical example.However, in some other embodiments, there will not be any dislocationdefects at the bottom portion when the lattice mismatch is small betweensubstrate and epi film, e.g., GaAs growth in Ge trench.

Further, there will be an upper portion 140 above the bottom portion 130where the large lattice mismatch epi layer like Ge crystal issubstantially defect free. Moreover, it is noted that dislocationdefects are not present on the side surfaces 108 since the large latticemismatch epi film growth from the side surfaces was prohibited by theetch component 120. Thus, the bottom-up growth process 110 trapsdislocation defects, if any, at the bottom portion 130 of the trench,and forms a substantially defect-free pure single crystal, e.g., Gestructure, at the upper portion 140 of the substrate, e.g., Si trench.Accordingly, the defect-free epi film structure like Ge crystal could beused either as a compressive or tensile strain stressor into thesubstrate 102 due to having a large or small lattice constant than thesubstrate or a transistor channel with or without a desired compressiveor tensile strain.

Although the discussion above uses pure Ge crystal as an example, thebottom-up growth technique may be implemented to grow other types ofcrystal structures such as silicon carbide (SiC) for NMOS devicestressor, III-V compound semiconductors such as GaAs and InSb can begrown in Si or Ge trench as channel materials. For SiC growth, theetchant component may be the same one used for Ge growth. For III-Vcompound semiconductors, the etch component may include Cl or Brcontaining gases.

Further, it is noted that other process parameters may be tuned tomodulate the growth rate on different crystal planes. For example,temperature, pressure, etching gas flow, carrying gas flow, anddeposition gas flow, and combinations thereof may be used to modulatethe growth rate. Moreover, the bottom-up growth technique is fullycompatible and can easily be integrated with current fabricationtechnologies such as CMOS technology processing.

Referring to FIG. 3, illustrated is a flow chart of a method 200 offabricating a semiconductor device according to various aspects of thepresent disclosure. The method 200 begins with block 202 in which asemiconductor substrate is provided. The method 200 continues with block204 in which a gate structure is formed on the substrate. The method 200continues with block 206 in spacers are formed on sidewalls of the gatestructure, respectively. The method continues with block 208 in which arecess is formed in the substrate at either side of the gate structure.The method 200 continues with block 210 in which a semiconductormaterial is epitaxially grown to fill the recess using bottom-up growththat incorporates an etch component. The method 200 continues with block212 in which fabrication of the semiconductor device is completed. Thediscussion that follows illustrates various embodiments of asemiconductor device that can be fabricated according to the method 200of FIG. 3.

Referring to FIGS. 4A-4F, illustrated is an embodiment of asemiconductor device 300 at various stages of fabrication according tothe method 200 of FIG. 3. It is understood that FIGS. 4A-4F have beensimplified for the sake of clarity to better understand the inventiveconcepts of the present disclosure. In FIG. 4A, the semiconductor device300 includes a substrate 302. The substrate 302 includes a siliconsubstrate. In another embodiment, the semiconductor substrate 302 mayinclude an epitaxial layer. For example, the substrate 302 may have anepitaxial layer overlying a bulk semiconductor. The substrate 302further includes doped regions such as p-wells and n-wells. Furthermore,the substrate 302 may include a semiconductor-on-insulator (SOI)structure such as a buried dielectric layer. Alternatively, thesubstrate 302 may include a buried dielectric layer such as a buriedoxide (BOX) layer, such as that formed by a method referred to asseparation by implantation of oxygen (SIMOX) technology, wafer bonding,selective epitaxial growth (SEG), or other proper method. Thesemiconductor device 300 includes active regions defined in thesubstrate 302.

Various shallow trench isolation (STI) structures 304 are formed in thesemiconductor substrate for isolating the various active regions. Theformation of STI may include etching a trench in a substrate and fillingthe trench by insulator materials such as silicon oxide, siliconnitride, or silicon oxynitride. The filled trench may have a multi-layerstructure such as a thermal oxide liner layer with silicon nitridefilling the trench. In one embodiment, the STI structure may be createdusing a process sequence such as: growing a pad oxide, forming a lowpressure chemical vapor deposition (LPCVD) nitride layer, patterning anSTI opening using photoresist and masking, etching a trench in thesubstrate, optionally growing a thermal oxide trench liner to improvethe trench interface, filling the trench with CVD oxide, using chemicalmechanical planarization (CMP) to etch back, and using nitride strippingto leave the STI structure.

One or more operational devices are formed in the active regions. Theoperational devices include n-type and p-type metal-oxide-semiconductorfield-effect transistors (NMOS and PMOS devices). The operationaldevices are configured as an array of NMOS devices and an array of PMOSdevices. The NMOS and PMOS devices may be fabricated by CMOS technologyprocessing. Accordingly, it is understood that additional processes maybe provided before, during, and after the method 200 of FIG. 3, and thatsome other processes may only be briefly described herein. Each NMOS andPMOS device includes a gate structure formed on the semiconductorsubstrate 302. The gate structure includes a gate dielectric 306 and agate electrode 308. The gate dielectric 306 may include silicon oxide,silicon nitride, high-k dielectric, or other suitable material. Thehigh-k dielectric layer may include a binary or ternary high-k film suchas HfOx. Alternatively, the high-k dielectric layer 306 may optionallyinclude other high-k dielectrics such as LaO, AlO, ZrO, TiO, Ta2O5,Y2O3, SrTiO3 (STO), BaTiO3 (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO,AlSiO, HfTaO, HfTiO, (Ba,Sr) TiO3 (BST), Al2O3, Si3N4, oxynitrides, orother suitable materials. The gate dielectric is formed by a suitableprocess such as an atomic layer deposition (ALD), chemical vapordeposition (CVD), physical vapor deposition (PVD), thermal oxidation,UV-ozone oxidation, or combinations thereof.

The gate electrode 308 may include polysilicon (or poly). For example,silane (SiH₄) may be used as a chemical gas in a CVD process to form thepoly. The poly layer may include a thickness ranging from about 400 toabout 800 Angstrom (Å). The gate structure may further include a hardmask layer 310 formed on the gate electrode 308. The hard mask layer 310include silicon oxide. Alternatively, the hard mask layer 310 mayoptionally silicon nitride, silicon oxynitride, and/or other suitabledielectric materials, and may be formed using a method such as CVD orPVD. The hard mask layer 310 may include a thickness ranging from about100 to about 400 Angstrom (Å).

The semiconductor device 300 includes an offset spacer 312 formed oneach sidewall of the gate structures. The offset spacer 312 may includesilicon oxide and silicon nitride. The offset spacer 312 may be formedby CVD, PVD, ALD, plasma enhanced CVD (PECVD), or other suitabletechnique. An ion implantation process may be performed to form lightlydoped source/drain regions (LDD) in the substrate 302 (not shown). Theion implantation process may utilize p-type dopants (e.g., B or In) forthe PMOS device and n-type dopants (P or As) for the NMOS device.

The semiconductor device 300 further includes an oxide layer 314 formedover the substrate 302 and the gate structures. The oxide layer may beformed by CVD, PVD, ALD, or other suitable technique. The oxide layer314 includes a thickness ranging from about 2 to about 4 nm. Thesemiconductor device 300 further includes a nitride layer 316 formedover the oxide layer 314. The nitride layer 316 may be formed of siliconnitride. The nitride layer 316 may be formed by CVD, PVD, ALD, or othersuitable technique. The nitride layer 316 includes a thickness rangingfrom about 10 to about 15 nm. The oxide layer 314 and nitride layer 316may be etched to form spacers that are used in the formation of thestrained source and drain features as discussed below. Accordingly, thethicknesses of the oxide layer 314 and the nitride layer 316 maydetermine how far the strained source and drain features will be spacedfrom a channel region of the PMOS device.

A patterned photoresist layer 320 is formed to protect the NMOS devices.The patterned photoresist layer 320 may be formed by a photolithographyprocess. An exemplary photolithography process may include processingsteps of photoresist coating, soft baking, mask aligning, exposing,post-exposure baking, developing photoresist and hard baking. Thephotolithography exposing process may also be implemented or replaced byother proper techniques such as maskless photolithography, electron-beamwriting, ion-beam writing, and molecular imprint.

In FIG. 4B, an etching process 324 is performed to remove portions ofthe nitride layer 316 directly overlying the substrate 302. In thepresent embodiment, the etching process 224 includes a dry etchingprocess that utilizes a gas combination of CHxFy/O2 or SF6/CHxFy/He(where x=1 to 3 and y=4−x) or other suitable gas combination. The dryetching provides directional etching (e.g., anisotropic etching) suchthat some portions of the nitride layer 316 a remain over the sidewallsof the gate structure following the etching process 324.

In FIG. 4C, an etching process 328 is performed to break through theoxide 314 directly overlying the substrate 302. The etching process 328includes a dry etching process that utilizes a gas combination ofCF4/Cl2/HBr/He or other suitable gas combination. Therefore, followingthe etching process 328, a portion of the oxide layer 314 a and thenitride layer 316 a remain of the sidewalls of the gate structure of thePMOS device thereby forming spacers 330.

In FIG. 4D, an etching process 332 is performed to etch a recess 340 inthe substrate 302. The etching process 332 includes a dry etchingprocess that utilizes a combination of HBr/Cl2/O2/He, a pressure rangingfrom about 1 mT to about 1000 mT, a power ranging from about 50 W toabout 1000 W, a bias voltage ranging from about 100 V to about 500 V, anHBr flow rate ranging from about 10 sccm to about 500 sccm, a Cl2 flowrate ranging from about 0 sccm to about 500 sccm, an O2 flow rateranging from about 0 sccm to about 100 sccm, and an He flow rate rangingfrom about 0 sccm to about 1000 sccm. The dry etching removes portionsof the silicon substrate 302 that are unprotected or exposed.Accordingly, the recess 340 has vertical sidewalls that are aligned withthe spacers 330 due to the directional/anisotropic etching. The recess340 may have a depth 342 ranging from about 400 to about 800 Angstrom(Å).

In FIG. 4E, an epitaxy (epi) process 350 is performed to deposit asemiconductor material in the recess 340. The patterned photoresist 320protecting the NMOS devices is removed prior to the epi process 350. Apre-cleaning process may be performed to clean the recess 340 with HF orother suitable solution. In the present embodiment, the epi process 350is similar to the bottom-up growth process 110 discussed with referenceto FIGS. 2A-2C. Accordingly, a pure Ge crystal structure 355 is grown inthe recess 340 to form strained source and drain features. It is notedthat there may be some dislocation defects that are trapped at a bottomportion 357 of the Ge structure 355, however these defects should notadversely impact the performance of the PMOS device. Additionally, insome embodiments, the Ge 355 is deposited such that it is raised adistance above the surface of the substrate 302.

As previously discussed, current SiGe structures that are implementedfor strained source and drain features are limited as to the amount ofstrain that can be generated. The concentration of Ge in the SiGestructure determines the amount of strain generated, and thus increasingthe Ge concentration will increase the amount of strain. However, the Geconcentration can only be increased up to a certain level so as toachieve a sufficient critical thickness for the strained SiGe structure.Here, in the present embodiment, defect-free pure Ge crystal is formedfor the strained source and drain features or high mobility channel. Assuch, the Ge crystal 355 will generate a significant amount ofcompressive strain (e.g., about 4 GPa or more) 359 to enhance holemobility and improve PMOS device performance on Si or SiGe substrate.Thus, other types of stressors such as contact etch stop layer (CESL)will no longer be needed since the Ge source and drain by itself willprovide more than 4 GPa compressive channel strain to achieve a maximumSi hole mobility. In furtherance of the present embodiment, the Ge 250may be in-situ doped with p-type impurities, such as B or In, to formsource and drain regions of the PMOS device.

In FIG. 4F, an etching process 360 is performed to remove the nitridelayer 316 overlying the NMOS device and nitride layer 316 a overlyingthe PMOS device. The etching process 360 includes a wet etchingutilizing H3PO4 or other suitable etchant. The wet etching is selectedso that a slow etch rate is achieved to protect the poly. Thesemiconductor device 300 continues with processing to completefabrication as discussed briefly below. For example, source/drainregions for the NMOS device may be formed by ion implantation of n-typedopants such as P or As. In another embodiment, silicon carbide (SiC)may be deposited in the silicon substrate trench to form thesource/drain regions of the NMOS device by the bottom-up growthtechnique as described above. Additionally, silicide features are formedon the raised source/drain features to reduce the contact resistance.The silicide can be formed on the sources/drains by a process includingdepositing a metal layer, annealing the metal layer such that the metallayer is able to react with silicon to form silicide, and then removingthe non-reacted metal layer.

An inter-level dielectric (ILD) layer is formed on the substrate and achemical mechanical polishing (CMP) process is further applied to thesubstrate to polish the substrate. In an embodiment, the gate electrode308 remains poly in the final device. In another embodiment, the poly isremoved and replaced with a metal in a gate last or gate replacementprocess. In a gate last process, the CMP process on the ILD layer iscontinued until the poly surface is exposed, and an etching process isperformed to remove the poly thereby forming trenches. The trenches arefilled with a proper work function metal (e.g., p-type work functionmetal and n-type work function metal) in the PMOS devices and the NMOSdevice. A multilayer interconnection (MLI) is formed on the substrate toelectrically connect various device features to form a integratedcircuit. The multilayer interconnection includes vertical interconnects,such as conventional vias or contacts, and horizontal interconnects,such as metal lines. The various interconnection features may implementvarious conductive materials including copper, tungsten and silicide. Inone example, a damascene process is used to form copper multilayerinterconnection structure.

Referring to FIGS. 5A-5D, illustrated is another embodiment of asemiconductor device 400 at various stages of fabrication according tovarious aspects of the present disclosure. The semiconductor device 400includes a FinFET element. It is understood that FIGS. 5A-5D have beensimplified to better understand the inventive concepts of the presentembodiment, and thus some known features and processes have beenomitted. In FIG. 5A, the semiconductor device 400 includes a substrate(not shown). The substrate may be silicon in a crystalline structure.The semiconductor device 400 includes a plurality of fins 404 thatextend from the substrate. Although only one fin is shown, it isunderstood that the number of fins may vary depending on the particularapplication. The fins 404 include silicon. The fins 404 may befabricated by using suitable process such as photolithography and etch.For example, the photolithography process may include forming aphotoresist layer (resist) overlying the substrate (e.g., on a siliconlayer), exposing the resist to a pattern, performing post-exposure bakeprocesses, and developing the resist to form a masking element includingthe resist. The masking element may then be used to etch fins 404 fromthe substrate. The fins 404 may be etched using reactive ion etch (RIE)and/or other suitable processes. Shallow trench isolation (STI)structures 406 surround the fins 404 and isolate each fin from the otherfins. The STI structures 406 may include any suitable insulatingmaterial.

In other embodiments, the substrate includes a silicon-on-insulator(SOI) substrate. The SOI substrate may be fabricated using separation byimplantation of oxygen (SIMOX), wafer bonding, and/or other suitablemethods. The layer of silicon may be a silicon layer of an SOI substrate(e.g., overlying an insulator layer). The fins may be formed, forexample, by etching a layer of silicon on the substrate.

The semiconductor device 400 includes multiple gate structures 408 thatare formed over a portion of the fins 404. The gate structures wraparound the fins 404 allowing gate control of the channel from both sidesof the fin. The gate structures 408 include a gate dielectric layer, agate electrode, and a hard mask similar to the ones discussed withreference to FIG. 4. Spacers 409 are formed on sidewalls of the gatestructured 408.

In FIG. 5B, an etching process 410 is performed remove exposed portionsof the fins 404. In the present embodiment, the etching process 410 issimilar to the etching process 332 of FIG. 4. Therefore, following theetching process 410, a recess 420 is formed. The recess 420 has a bottomsurface 422 with a first crystal plane orientation (e.g., [100]) and aside surface 424 with a second crystal plane orientation (e.g., [110]).It is noted that the STI 406 forms the other sides of the recess 420.

In FIG. 5C, an epitaxial (epi) growth process 430 is performed todeposit a semiconductor material in the recess 420. In the presentembodiment, the epi process 430 is similar to the bottom-up growthprocess 110 discussed with reference to FIGS. 2A-2C. The Ge growth rateon the first crystal plane orientation (bottom surface 422) is greaterthan the growth rate on the second crystal plane orientation (sidesurface 424). As discussed above, an etch component controls andprohibits growth on the side surface 424 during the epi process 430.Further, the etch component may remove Ge that may be disposed on thesides of the STI 406. Accordingly, a pure Ge crystal structure 440 issubstantially grown in the recess 420 from the bottom-up. The bottom-upgrowth continues up to the STI 406 surface. In FIG. 5D, the bottom-upgrowth continues beyond the surface of the STI 406 and is completed toform the Ge structure 440 to a desired height. The Ge structure 440 ofthe strained source and drain features enhances hole mobility whichimproves device performance.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.For example, other epi films may be grown in the silicon trench forchannel materials such as Ge or III-V compound semiconductors.

What is claimed is:
 1. A method of fabricating a semiconductor device,comprising: providing a semiconductor substrate; forming a trench in thesubstrate, wherein a bottom surface of the trench has a first crystalplane orientation and a side surface of the trench has a second crystalplane orientation; and epitaxially (epi) growing a semiconductormaterial in the trench; wherein the epi process utilizes an etchcomponent, and wherein a first growth rate on the first crystal planeorientation is greater than a second growth rate on the second crystalplane orientation.
 2. The method of claim 1, wherein the semiconductormaterial includes one of silicon (Si), silicon germanium (SiGe),germanium (Ge), silicon carbide (SiC), and III-V compound semiconductor.3. The method of claim 1, wherein the etch component includes one of aCl containing gas and a Br containing gas.
 4. The method of claim 1,wherein the substrate includes one of silicon (Si) and germanium (Ge).5. The method of claim 1, wherein the first crystal plane orientationincludes [100] and wherein the second crystal plane orientation includesone of [110] and [111].
 6. The method of claim 2, wherein the III-Vcompound semiconductor includes one of GaAs and InSb.
 7. The method ofclaim 3, wherein the etch component includes HCl.
 8. A method offabricating a semiconductor device, comprising: forming a transistor ona semiconductor substrate including: a gate structure disposed over thesubstrate; a trench in the semiconductor substrate adjacent the gatestructure, wherein a bottom surface of the trench has a first crystalplane orientation of the substrate, and two opposing side surfaces ofthe trench have a second crystal plane orientation of the substrate, thefirst crystal plane orientation being different from the second crystalplane orientation; and a strained feature formed within the trench onthe substrate, wherein the strained feature is formed by growing an epifilm by a bottom-up growth process such that the epi is grownpredominately from the bottom surface of a trench in the semiconductorsubstrate and a side surface of the epi-film is substantially free ofdislocation defects.
 9. The method of claim 8, wherein the first crystalplane orientation includes [100] and wherein the second crystal planeorientation includes one of [110] and [111].
 10. The method of claim 9,wherein the epi film includes Ge and wherein the transistor includes aPMOS device.
 11. The method of claim 10, wherein the transistor includesa FinFET and wherein the strained feature forms a portion of a fin. 12.The method device of claim 10, wherein the transistor includes a planarFET.
 13. A method of fabricating a semiconductor device, comprising:providing a semiconductor substrate; forming a trench in the substrate,wherein a first surface of the trench has a first crystal planeorientation and a second surface of the trench has a second crystalplane orientation; and performing an epitaxial (epi) growth process togrow an epi film in the trench, the epi growth process incorporating anetch component; wherein a first growth rate on the first crystal planeorientation is different from a second growth rate on the second crystalplane orientation such that the etch component prohibits growth on oneof the first and second crystal plane orientations.
 14. The method ofclaim 13, wherein the first growth rate is greater than the secondgrowth rate.
 15. The method of claim 13, wherein the semiconductormaterial includes one of silicon (Si), silicon germanium (SiGe),germanium (Ge), silicon carbide (SiC), and III-V compound semiconductor.16. The method of claim 15, wherein the semiconductor substrate includessilicon (Si).
 17. The method of claim 16, wherein the etch componentincludes one of a Cl containing gas and a Br containing gas.